The long range goal of this project is to understand the functional organization of the vaccinia virus genome. To this end, we propose to expand our existing collection of ts mutants of vaccinia, construct a physical map of the mutants on the virus genome using marker rescue and recombination analysis, research drug selection techniques for isolating mutants in specific virus genes, and conduct a detailed biochemical analysis of existing mutants showing defects in regulation of virus gene expression. The project is designed to provide information about the regulation of viral gene expression in general and ultimately to study the role of several interesting mRNA metabolism enzymesin eucaryotic gene expression. In addition, since the genomes of the orthopoxvirus group can collectively be broken down into conserved and variable regions, an understanding of the functional organization of the vaccinia genome should provide insights into factors affecting virus host range and pathogenecity.